Gallium nitride-based III-V group nitride, which is attracting attention as an excellent blue light emitting element, is put into practical use in light emitting diode, and expected also as a blue-violet semiconductor laser element for light pick-up. According to the method of growing GaN single crystal, described in “Jpn. J. Appl. Phys.” Vol. 42 (2003), pp. L879-L881, a boron nitride growth vessel is placed within a pressure-resistant container, metal Ga of group-III raw material and Na as flux are put in the boron nitride growth vessel, and nitrogen gas is supplied into the pressure-resistant container at high pressure. Nitrogen of group-V raw material is dissolved to a Ga—Na mixed melt under heating and pressurizing to thereby grow the GaN single crystal on a seed crystal substrate within the growth vessel. In that case, the boron nitride growth vessel is oscillated by mounting a rotary shaft on an electric furnace containing the boron nitride growth vessel, connecting the rotary shaft to a motor shaft, and operating the motor.